Computer simulations of the mixing of a pair of Bose-Einstein condensates (atomic gases cooled to their quantum ground states) reveal a “fingering” pattern previously seen only in classical fluids, such as in a lava lamp. A team of theorists produced the simulations as a demonstration of the surprising patterns that can form spontaneously in a quantum system.

K.-T. Xi et al., Phys. Rev. A (2018)

Spin-up (left) and spin-down (right) Bose-Einstein condensates form a fingering pattern when interacting. The dipole-dipole repulsion is weak, about one-fifth of the strength of the interaction in the video below.

K.-T. Xi et al., Phys. Rev. A (2018)

Same as above, but here the dipole-dipole interaction is about 5 times as strong.

The researchers, led by Hiroki Saito of the University of Electro-Communications in Tokyo, simulated two condensates whose atoms are the same except that they have magnetic dipole moments (internal “bar magnets”) pointing in opposite directions. Initially, magnetic interactions are turned off, and the condensates are arranged in the pancake-shaped trap with one sitting in a central disk and the other forming a surrounding ring. At the start of the two simulations shown above, the magnetic (dipole) interaction force is suddenly switched on, so that—in the classical view—each atom behaves like a bar magnet that is either aligned or anti-aligned with each of its neighbors. The strength of this interdipole force determines the size of the fingers that appear, as shown by the two videos.

The researchers say that their simulations could be brought to life using chromium atoms and standard manipulations with magnetic fields.